Subsea wellheads in iceberg prone areas are susceptible to damage by iceberg scouring. Efforts have been made to protect such wellhead assemblies from iceberg scouring by excavating and placing the wellhead assembly in the excavation as shown in U.S. Pat. Nos. 3,461,951 and 3,952,263. In some cases covers, shields and anchor devices are used to protect the subsea wellhead as disclosed in U.S. Pat. No. 4,220,421.
Another prior art disclosure of a solution to solve iceberg scouring problems is suggested in the January 1980 issue of Ocean Industry page 19 et seq. in an article entitled "A Seasonal Oil Production Scheme for Iceberg infested Waters." A silo is lowered into a subsea excavation and the production Christmas tree is installed therein five meters below the mud line. The casings are hung in a caisson 17 meters below the bottom of the silo. A weak point is provided above the upper master valve " . . . as a safety measure in the improbable case where an iceberg would scour the bottom to a depth greater than the maximum depth foreseen, and would touch the silo or the top of the wellhead. The breakage of the weak point in this case, would assure the integrity of the two master valve blocks and, therefore, the safety of the well." Such weak point is in the production lines above the upper block valves.
One problem not considered in these prior attempts to preserve a subsea well that has been subject to a deep iceberg damage is that merely providing for a weak point in the production lines may not preserve the well when the conductor pipe is damaged.